Compositions containing a bisphenol A-type epoxy resin excellent in adhesiveness and/or mechanical strength, an epoxy resin free from UV absorption, for example, a hydrogenated bisphenol A-type epoxy resin or an alicyclic epoxy resin, a curing agent, and a curing catalyst are frequently used as resin compositions for optical semiconductor device sealing. Such compositions, however, disadvantageously cause discoloration or cracks due to light, heat, or the like from LED devices, as the luminance and output of the LED devices are increased.
To solve these problems, a resin has been known which contains an epoxy group introduced into a silicone resin that offers a UV absorption-free and flexible cured product. For example, the following has been known: a silicone resin having one or more cyclic ether-containing groups such as a glycidyl group and an epoxycyclohexyl group (JP 2008-45088), a reaction product of epoxyalkoxysilane and silanol (JP H7-97433), and an alicyclic epoxy-modified silicone resin used in combination with an alicyclic epoxy resin (JP 2006-282988). Silicone resins, however, are very highly permeable to gas as compared with epoxy resins. Therefore, products having a higher silicone content are more difficult to use in usage required to have low permeability to gas. Accordingly, an addition reaction-type phenyl-based silicone resin composition has been disclosed as a resin composition having low permeability to gas (JP 2002-265787), but is still unsatisfactory in terms of low permeability to gas and adhesiveness. In addition, an epoxy resin composition obtained using epoxy group-containing polysiloxane and a carboxylic anhydride compound as a curing agent for the polysiloxane has been disclosed (JP 2012-92172), but is unsatisfactory from the viewpoint of the heat discoloration resistance of a cured product.